1. Field of the Invention
The present invention relates to a zeolite, hereinafter referred to as zeolite GZS-11, to a dynamic synthetic method of making it, and to processes using it as a catalyst.
2. Discussion of the Prior Art
The synthesis of molecular sieves involves a variety of parameters, including gel composition, reaction temperature and pressure, reaction time, and the state of the synthesis gel (static or stirring, and stirring rate). Among these parameters, gel composition is probably the most significant, which contains important variables such as silicon/aluminum ratio, hydroxide concentration, inorganic and/or organic cation, and which determines in large part the structure and composition of the molecular sieve product. In the conventional synthesis of molecular sieves, the gel composition is defined at the very early stage when a synthesis gel is prepared. There has not been an intentional alteration of the gel composition during the aging of a synthesis gel until the formation of a molecular sieve is completed.
Post-treatment has been used to modify the composition of molecular sieves. U.S. Pat. No. 4,503,023 describes a process of extracting aluminum from AlO.sub.4 -tetrahedra of as-synthesized zeolite and substituting with silicon to form zeolite compositions having higher SiO.sub.2 /Al2O.sub.3 molar ratios. For example, zeolite Y has been treated by reacting with a solution containing (NH.sub.4).sub.2 SiF.sub.6 to form LZ-210.
In contrast to these prior art techniques, the invention uses a gel composition which has its composition changed during the aging step to effectively alter the composition of the final product. By using this process unique forms of zeolite beta are made.
Zeolite beta and its hydrothermal synthesis were first disclosed in U.S. Pat. No. 3,308,069, issued Mar. 7, 1967, to R. L. Wadlinger et al. As disclosed therein, zeolite beta has a chemical composition in its as-synthesized form expressed in terms of molar oxide ratios of EQU [x Na.sub.2 O+(1.0.+-.0.1-x)TEA.sub.2 O]:Al.sub.2 O.sub.3 :y SiO.sub.2 :w H.sub.2 O
where "x" has a value of less than 1.0, "y" has a value of greater than 10 but less than 200, "w" has a value of up to 4 depending upon the degree of hydration of the zeolite, and TEA represents tetraethylammonium ion. The zeolite is said to be formed by crystallization at temperatures in the range of 75.degree. C. to 200.degree. C., from an aqueous reaction mixture containing tetraethylammonium hydroxide and reactive sources of Na.sub.2 O, Al.sub.2 O.sub.3, and SiO.sub.2, with a composition of the reaction mixture, expressed in terms of mol ratios of oxides, within the following ranges:
SiO.sub.2 /Al.sub.2 O.sub.3 10 to 200 PA1 Na.sub.2 O/TEAOH 0 to 0.1 PA1 TEAOH/SiO.sub.2 0.1 to 1.0 PA1 H.sub.2 O/TEAOH 20 to 75 PA1 SiO.sub.2 /Al.sub.2 O.sub.3 5 to 250 PA1 H.sub.2 O/SiO.sub.2 10 to 100 PA1 OH.sup.- /SiO.sub.2 0.09 to 0.8 PA1 R/(R+M) 0.1 to 0.8 PA1 (1) Prepare a synthesis gel mixture by mixing sources of inorganic reactants and organic structural directing agents. Reactive sources of aluminum, silicon and alkali metal include aluminates, aluminas, silicates, silica hydrosols, reactive amorphous solid silicas, silica gel, tetraalkylorthosilicates, silicic acid and alkali metal hydroxides. Organic structural directing agents include tetraalkylammonium ions, trialkylammonium ions, dialkylammonium ions, monoalkylammonium ions, amines with same or different alkyl groups, tetraalkylphosphonium ions, to list a few. The initial composition is determined to favor the nucleation of the desired zeolite. PA1 (2) Heat the gel mixture, with or without stirring, to a desired temperature and age at that temperature for a specified length of time until nucleation and initial crystallization begin. The nucleation and initial crystallization can be monitored by any suitable analytical technique, such as MAS NMR, XRD and IR. PA1 (3) Once crystallization has begun, add one or more solutions which contain one or more reactants into the reaction mixture over a predetermined length of time. These solutions can be prepared using inorganic and organic reagents, and may include structural directing agents. During this stage, the composition of the liquid phase of the reaction mixture is slowly changed while the crystals of the desired zeolite are growing. Care needs to be taken to control the rate of solution addition so that the crystallization process is not interrupted by a sudden change of the composition of the liquid phase. The total amount of each solution to be added may also be limited for a specific zeolite. Beyond this limit other impurity phases may form. PA1 (4) Continue aging the mixture, with or without stirring, at a specified temperature for a specified length of time. This step allows the completion of crystallization of a zeolite. PA1 (5) Stop aging after the zeolite formation is completed, and collect the crystalline product by filtration or centrifugation, washing, and drying. PA1 (1) Prepare an initial gel mixture which contains sources of, for example, alkali or alkaline earth metal (M), e.g. sodium or potassium, cation if desired, one or a combination of oxides selected from the group consisting of trivalent element X, e.g. aluminum, tetravalent element Y, e.g. silicon, one or more organic (R) directing agents, e.g. tetraethylammonium hydroxide and/or halides, and a solvent or solvent mixture, e.g. water, said gel mixture having a composition, in terms of mole ratios, within the following ranges: PA1 XO.sub.2 /Y.sub.2 O.sub.3 =18-100 PA1 M.sub.2 O/Y.sub.2 O.sub.3 =0.5-5 PA1 (R.sub.2 O+M.sub.2 O)/Y.sub.2 O.sub.3 =1-15 PA1 H.sub.2 O/(Y.sub.2 O.sub.3 +XO.sub.2 +M.sub.2 O+R.sub.2 O)=1-50 PA1 (2) Age the gel mixture at a temperature between 50.degree. C. and 200.degree. C. under atmospheric or autogenous pressure for from 2 hours to 10 days, with or without stirring. PA1 (3) Add to the reaction mixture one or more solutions which may contain monovalent element, e.g. sodium, trivalent element, e.g. aluminum, and/or tetravalent element, e.g. silicon, and/or organic directing agent, e.g. tetraethylammonium hydroxide or halide. The addition solutions and the rates of additions should be carefully selected so that the overall concentration of OH does not change dramatically from the pH of the initial gel mixture. PA1 (4) After the completion of the addition, continue to age the mixture at a temperature between 50.degree. and 200.degree. C. for between 0.1 to 10 days. PA1 (5) Cool down the reaction mixture to room temperature and collect GZS-11 crystals by centrifuging or filtering the solid, washing with water and drying at 100.degree. C.
The more significant interplanar d-spacing of zeolite beta, dried in air at 110.degree. C., are listed in Table A, below:
TABLE A ______________________________________ Interplanar Relative d-Spacing (.ANG.) Intensity (I/I.sub.o) ______________________________________ 11.5 .+-. 0.4 M-S 7.4 .+-. 0.2 W 6.6 .+-. 0.15 W 4.15 .+-. 0.10 W 3.97 .+-. 0.10 VS 3.00 .+-. 0.07 W 2.05 .+-. 0.05 W ______________________________________
The lowest silica/alumina ratio of 13.9 for zeolite beta is described in Example 1 of U.S. Pat. No. 3,308,069. Zeolite beta having silica/alumina ratio of 13.9 was prepared from a reaction gel mixture held at 78.degree. C. for 42 days.
European Pat. Appl. No. 55,046 describes the synthesis of zeolite Nu-2, a member of the zeolite-beta family of zeolites, from reaction mixtures containing tetraethylammonium ion as the structural directing agent. Zeolite Nu-2 can only be prepared in pure form with products having SiO.sub.2 /Al.sub.2 O.sub.3 ratios from 20 to about 50.
In a later synthesis of zeolite beta, disclosed in U.S. Pat. No. 4,554,145, the organic directing agent employed is derived from dibenzyl-1,4-diazabicyclo[2,2,2]octane chloride. The synthesis involves the preparation of a reaction mixture containing sources of alkali metal oxide, an oxide of alumina, an oxide of silica, water, and the cation of the aforementioned organic compound in proportions within the following ranges:
where R represents the organic cation and M represents the alkali metal cation. The quantity of OH.sup.- ion is calculated using only the contribution of inorganic alkali. In the two specific examples disclosed, crystallization of the zeolite beta is accomplished at 99.degree. and 100.degree. C. over periods of 119 and 169 days, respectively. Zeolite P and mordenite types of crystalline impurities are found in the products along with zeolite beta.
In U.S. Pat. No. 4,642,226 the synthesis of zeolite beta using dibenzyldimethylammonium ion as the directing agent is disclosed. The organic cations are derived from dibenzyldimethylammonium chloride added to the reaction mixture per se or produced therein in situ by the reaction of benzyl chloride with dimethylbenzylamine. It is stated that the composition of the reaction mixture is critical with respect to the presence of alkali-derived OH.sup.- groups and the SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio.
U.S. Pat. No. 4,923,690 discloses a synthesis process of zeolite beta which uses a mixture of tetraethylammonium halide and tetraethylammonium hydroxide as the directing agent. Either the hydroxide or the halide salt used alone is also reported to yield a zeolite beta-containing product which is 30% to 90% crystalline of which zeolite beta can constitute essentially all or some minor portion thereof.
U.S. Pat. No. 5,139,759 discloses a hydrothermal synthesis of zeolite beta from an aqueous reaction mixture containing the conventional reactive sources of SiO.sub.2, Al.sub.2 O.sub.3 and Na.sub.2 O,and tetraethylammonium halide as the source of the crystallization directing agent and diethanolamine as the agent providing the increased basicity necessary for formation of zeolite beta crystals. Seed crystals of zeolite beta are optionally employed to shorten the crystallization period. The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the synthesized zeolite beta is claimed in the range of 10 to 200, and the ratios of 23.6 and 22.8 are obtained in the two examples.
U.S. Pat. Nos. 5,164,169 and 5,164,170 describe the synthesis of beta zeolite with triethanolamine and directing agents such as tetraethylammonium hydroxide, tetraethylammonium bromide, and tetraethylammonium fluoride. The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the zeolite beta ranges from 20 to 200.
U.S. Pat. No. 5,171,556 reveals a beta type zeolite prepared in a fluoride medium and the zeolite contains fluorine whose content ranges from 0.005 to 2.0% by weight.
Perez-Pariente et al studied the factors affecting the synthesis of zeolite beta from aluminosilicate gels containing alkali and tetraethylammonium ions (Zeolites, 8(1988), 46). The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the synthesis gel is varied from 30 to 900, resulting in the SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the zeolite in the range of 22 to 86. As the crystallization proceeds, the SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the liquid phase increases and the final ratio can be as high as 30,000.
Camblor et al discussed the effect of sodium and potassium in the synthesis of zeolite beta (Zeolites, 11(1991), 202). They found that the lowest Si/Al ratios for zeolite beta are near 13 in all cases. At the end of the crystallization, the solution phase of the reaction mixture has a SiO.sub.2 /Al.sub.2 O.sub.3 ratio as high as &gt;10,000.
Caullet et al reported (Zeolites, 12(1992), 240) the synthesis of zeolite beta from nonalkaline fluoride aqueous aluminosilicate gels containing diaza-1,4-bicyclo [2.2.2] octane (DABCO) and methylamine as the templates. Zeolite beta is obtained from the gel mixtures having the following gel compositions: EQU 5-60 SiO.sub.2 :1 Al.sub.2 O.sub.3 :1 DABCO:1 CH.sub.3 NH.sub.2 :2 HF:10 H.sub.2 O
held at a temperature of between 150.degree. and 200.degree. C. for 7 to 21 days. Full transformation of the gel into zeolite beta requires the presence of seed crystals of preformed zeolite beta. The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of zeolite beta produced ranges from ca. 18 to 44.
Other synthesis of zeolite beta using tetraethylammonium ion as the template can be found in the following publications: Appl. Catal. 31(1987), 35; Appl. Catal. 69(1991), 49; Zeolites 11(1991), 792; Zeolites 12(1992), 280; J. Chem. Tech. Biotechnol. 48(1990), 453.
Boron beta zeolite has been made using a diquaternary ion as a template. U.S. Pat. No. 5,166,111 discloses a synthesis of low-aluminum boron beta zeolite in which aluminum content is less than 0.1% by weight and the ratio of YO.sub.2 /W.sub.2 O.sub.3 is greater than 10, where Y is selected from silicon, germanium, and mixtures thereof, W is boron or mixtures of boron with aluminum, gallium, or iron.
Gallium beta zeolite has been reported in the literature. Liu et al. described the galliation of beta to form gallium beta (Zeolites, 12(1992), 936). Hegde et al. reported the direct synthesis of gallium beta zeolite and studied it by FT i.r spectroscopy (Zeolites, 12(1992), 951).
The framework structure of zeolite beta has been thoroughly investigated by Newsam et al. using primarily high-resolution electron microscopy, electron diffraction, computer-assisted modelling and powder X-ray diffraction (Proc. B. Soc. Lond. A 4, 375 (1988)). Zeolite beta can be regarded as a highly intergrown hybrid of two distinct, but closely related structures that both have fully three-dimensional pore systems with 12-rings as the minimum constricting apertures. Other groups have studied the structure of beta zeolite as well and obtained similar conclusions. See publications: J. Chem. Soc. Chem. Comm. 1990, 813; Zeolites, 8(1988), 446.
Zeolite beta is useful as a catalyst and/or as an adsorbent. U.S. Pat. No. 4,898,846 describes the use of zeolite beta as an component for catalytic cracking catalysts. The as-synthesized zeolite beta is exchanged with ammonium and is calcined at temperatures high enough to decompose ammonium to proton. The H-form of zeolite beta is mixed with other components to form cracking catalysts which exhibit advantageous properties for converting petroleum into gasoline.
U.S. Pat. No. 4,740,292 describes the use of zeolite beta as a cracking component in the conversion of heavy oil to light products. This leads to higher octane gasoline, increased yields of propylene and butene, and a low pour point distillate product.
U.S. Pat. No. 5,160,033 describes a catalyst composition for a hydrocracking process. The catalyst is a combination of a steam-stabilized form of zeolite Y and a form of zeolite beta which has been modified to maximize the weak acid sites and minimize the strong acid sites.
While prior art has described the synthesis of zeolite beta, the claimed low limit of SiO.sub.2 /Al.sub.2 O.sub.3 ratio of this zeolite is above 10. In practice the lowest SiO.sub.2 /Al.sub.2 O.sub.3 ratio ever achieved for zeolite beta using the conventional synthetic process is around 14. A beta-like zeolite with a low SiO.sub.2 /Al.sub.2 O.sub.3 ratio of, for example, 10 may possess some advantages over the regular zeolite beta as a catalyst and/or an adsorbent.
It is therefore an object of this invention to disclose a new zeolite, GZS-11, which has a SiO.sub.2 /Al.sub.2 O.sub.3 ratio between 6 to 25 and which possesses a structure similar to that of zeolite beta.
It is a further object of this invention to teach a novel procedure for zeolite synthesis. By using this procedure, the composition of zeolites can be altered conveniently.
It is a further object of this invention to use the zeolite prepared in the instant invention as a component of catalysts and adsorbents.
These and further objects of the present invention will become readily apparent to one skilled in the art as the description of the invention proceeds.